MLXXXp: Thanks for showing your mod! I have the graphical version of that tester and it would be nice to upgrade it.
I mostly built my bangood kit (with case and rotary encoder) over the weekend. I prepared by doing a 4-wire measurement of the provided 0.1% 470K and 680 Ohm resistors. All were within spec, but I still paired them up so each was as close to the ideal ratio as possible. The value of this exercise is questionable, but I did it for fun.
I've paused to consider what I'm going to do about the test socket and leads. My current plan is to modify the case to shoehorn in three 2mm banana jacks rather than 2 4mm. Then I'm going to mount the DIP ZIF socket on a piece of protoboard and bolt/solder three 2mm banana plugs to the other side along one edge. It will be similar to the MK168/MK328. If I like the result, I'll probably have a small PCB made with some SMD test pads.
Parts are on order from China. At least some of them will be here within a week or so. I'll share details of my success (or failure!) once they arrive.
The other alternative I'm considering is to use some IC sockets as a riser to mount the ZIF socket onboard as giovannirat did and cut the case for it. Then, I'd make up an adapter that will allow 3 test leads.
Question: What, if any, downsides are there to replacing the 8MHz crystal with a 16MHz (and reflashing the MCU appropriately)? I figured the extra clock speed could help with UI responsiveness/refresh. Battery life might suffer, but I'd be ok with that.